Methods of making and using a superabsorbent polymer product including a bioactive, growth-promoting additive

ABSTRACT

A method of and a product formed by entrapping a bioactive, growth-promoting additive in a starch matrix to form a starch-based, superabsorbent polymer product for use in agricultural applications involves (1) graft polymerizing a monomer and a starch to form a starch graft copolymer including a starch matrix; (2) isolating the starch graft copolymer; (3) forming particles of starch graft copolymer; and (4) adding a bioactive, growth-promoting additive such that at least some of the bioactive, growth-promoting additive is entrapped by the starch matrix. Following placement of the starch-based SAP including a bioactive, growth-promoting additive in proximity to a plant, root, seed, or seedling, growth of the plant, root, seed, or seedling is promoted because availability of beneficial nutrients is increased.

RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Patent Application No. 60/529,949, filed Dec. 15, 2003.

TECHNICAL FIELD

The present invention relates to agricultural amendments, and moreparticularly to methods of making and using a superabsorbent polymerproduct including a bioactive, growth-promoting additive.

BACKGROUND INFORMATION

Over the past three decades, polymer chemists and soil scientists havedeveloped controlled-release pesticides for agricultural use. The twoprimary goals of controlled-release pesticides are (1) to increaseefficacy of the pesticide and (2) to reduce negative environmentalconsequences of pesticide application. Some prior art controlled-releasepesticides have been encapsulated in starch. These prior artstarch-encapsulated controlled-release pesticide products are typicallyformed by mixing starch and pesticides and forming balls of the mixture.These starch-encapsulated pesticides provide rate-limited release of thepesticide particles from the starch, which release is governed largelyby diffusion. Specifically, when starch-encapsulated pesticides areapplied to the soil, they imbibe water and swell such that the pesticideparticles diffuse out of the starch matrix into the soil surrounding aplant, root, seed, or seedling.

In 1976, polymer chemists developed a class of materials referred to assuperabsorbent polymers (SAPs) (see, e.g., U.S. Pat. Nos. 3,935,099;3,981,100; 3,985,616; and 3,997,484, all issued in 1976). SAPs arematerials that imbibe or absorb at least 10 times their own weight inaqueous fluid and that retain the imbibed or absorbed aqueous fluidunder moderate pressure. The imbibed or absorbed aqueous fluid is takeninto the molecular structure of the SAP rather then being contained inpores from which the fluid could be eliminated by squeezing. Some SAPscan absorb up to 1,000 times their weight in aqueous fluid.

One type of SAPs, called “totally synthetic copolymers,” is made bycopolymerizing acrylic acid and acrylamide in the presence of a couplingagent. Almost all totally synthetic copolymer SAPs are used in babydiapers, adult diapers, catamenials, hospital bed pads, cable coating,and the like. Today the worldwide market for totally synthetic copolymerSAPs is estimated to be about 2 billion pounds per year.

Another type of SAPs, called starch graft copolymers, use a naturalpolymer, such as a starch, to form an SAP product including a starchgraft copolymer. Films of starch graft copolymer SAP are typicallyformed by drying the starch graft copolymer composition on a tray orheating the composition on a drum dryer. The resulting films can then beground or milled into flakes or powders. Films of starch graft copolymerSAP may also be made by diluting a viscous mixture of alkali starchgraft copolymer with a water-miscible organic solvent such as alcohol oracetone to precipitate an alkali starch graft copolymer. Theprecipitated alkali starch graft copolymer is then isolated in a fine,powdery form by filtration and additional drying. Starch graft copolymerSAP products that absorb large quantities of aqueous fluids aretypically marketed as absorbent soft goods that increase thewater-holding capacity of soil and that form a coating on fibers, clay,paper, and the like.

The aqueous fluid absorption capabilities of SAPs have long made themdesirable to agricultural companies. However, testing of the totallysynthetic copolymer SAPs and the film or powdery starch graft copolymerSAPs showed poor agricultural performance, largely due to the particlesize of the SAP products (small, fine particles measuring about 80 meshin size). One inherent limitation of finer-mesh particles is that theycannot be used in typical granule applicators, which require particlesizes of at least 25 mesh. Further, the fine powders and/or films areoften carried away by any wind present during application of the SAPproduct onto a field or a growing substrate.

While pesticide particles mixed with starch have been manufactured formany years, no one has successfully entrapped pesticides in astarch-based SAP product appropriate for use in large-scale agriculturalapplications. The inventors of the present invention recognized a needin the agricultural industry for a method of forming a starch-based SAPproduct including a bioactive, growth-promoting additive whoseapplication to plants, roots, seedling, or seeds, or to a growingsubstrate in proximity to plants, roots, seedling, or seeds, promotesgrowth of the plants, roots, seedling, or seeds.

SUMMARY

One object of the present invention is to formulate a method ofproducing and using in agricultural applications a starch-based SAPproduct that includes a bioactive, growth-promoting additive.Application of the resulting SAP product promotes growth of a plant,root, seedling, or seed placed in proximity to the SAP product.

Preferred embodiments of the present invention generally relate tomethods of and products formed by entrapping particles of bioactive,growth-promoting additive in a starch matrix to form a starch-based SAPproduct including a bioactive, growth-promoting additive for use inlarge-scale agricultural applications. Following application of thestarch-based SAP product to a plant, root, seed, or seedling, or to agrowing substrate in proximity to a plant, root, seed, or seedling, thestarch-based SAP product promotes the availability of beneficialnutrients to the plant, root, seed, or seedling. Increasing theavailability of these nutrients effects an increase in crop yield,growth rate, seed germination, and/or plant size. The bioactive,growth-promoting additive is physically held by and taken into thestarch matrix portion of the SAP product, thereby forming a stable SAPproduct and minimizing or eliminating runoff of the additive duringheavy rainfall, squeezing, or jarring during transport. It is believedthat plants, roots, and seedlings withdraw the active portion of thebioactive, growth-promoting additive from the starch-based SAP productthrough capillary action, and that seeds utilize the bioactive,growth-promoting additive by diffusion of the additive from the starchmatrix.

A preferred method of forming an SAP product including a bioactive,growth-promoting additive involves (1) graft polymerizing at least onegrafting reagent and a starch to form a starch graft copolymer includinga starch matrix; (2) isolating the resulting starch graft copolymer; (3)forming films, powders, or particles of starch graft copolymer that aresized for use in agricultural applications; and (4) adding thebioactive, growth-promoting additive so that at least some of thebioactive, growth-promoting additive is entrapped by the starch matrix.Addition of the bioactive, growth-promoting additive may occur atvarious times during this process, depending on the type of additive andthe desired degree of entrapment of the additive within the starchmatrix.

There are at least two preferred implementations of this preferredmethod of forming the starch-based SAP product including a bioactive,growth-promoting additive. A first preferred implementation involves (1)combining a monomer and a starch in the presence of an initiator suchthat the monomer graft polymerizes onto the starch to form a mixtureincluding a starch graft copolymer having a starch matrix; (2)saponifying the mixture; (3) precipitating the saponified starch graftcopolymer from the mixture to form particles of SAP product that aresized for use in agricultural applications; and (4) adding thebioactive, growth-promoting additive so that at least some of thebioactive, growth-promoting additive is entrapped by the starch matrix.Addition of the bioactive, growth-promoting additive may occur, forexample, during at least one of the following processing steps: (1)while combining the monomer and the starch; (2) following saponificationof the starch graft copolymer; and (3) following formation of thestarch-based SAP product.

A second preferred implementation of the preferred method involves (1)graft polymerizing a monomer onto a starch in the presence of aninitiator to form a mixture including a starch graft copolymer having astarch matrix; (2) adding a cross-linking agent to the mixture tocross-link the starch graft copolymer; (3) neutralizing the mixture; (4)precipitating or isolating the cross-linked starch graft copolymer toform particles of SAP product that are sized for use in agriculturalapplications; and (5) adding the bioactive, growth-promoting additive sothat the bioactive, growth-promoting additive is entrapped by the starchmatrix. Addition of the bioactive, growth-promoting additive may occur,for example, during at least one of the following processing steps: (1)while graft polymerizing the monomer onto the starch; (2) followingneutralization; and (3) following formation of the particles ofstarch-based SAP product.

Preferred exemplary methods of using the starch-based SAP productincluding a bioactive, growth-promoting additive to promote plant, seed,seedling, or root growth include (1) placing the starch-based SAPproduct including a bioactive, growth-promoting additive (or a slurry,mat, or fertilizer including the SAP product) directly onto a growingsubstrate in proximity to a plant, seed, seedling, or root and (2)applying to a plant, seed, seedling, or root the starch-based SAPproduct (or a slurry, or fertilizer including the SAP product) and thenplanting the plant, root, seed, or seedling in the growing substrate.Application of the starch-based SAP product including a bioactive,growth-promoting additive directly to the soil or to a plant, seed,seedling, or root may result in earlier seed germination and/orblooming, decreased irrigation requirements, increased propagation,increased crop growth, increased crop production, and decreased soilcrusting. Thus the SAP products made by the above-described methodsoffer various advantages over prior art SAP products and methods offorming and using SAP products in large-scale agriculture.

Exemplary bioactive, growth-promoting additives include fertilizers,pesticides, bioactive materials, plant-growth hormones, and soil-basednutrients. A list of exemplary pesticides includes acaricides,algicides, antifeedants, avicides, bactericides, bird repellents,chemosterilants, fungicides, herbicide safeners, herbicides, insectattractants, insect repellents, insecticides, mammal repellents, matingdisruptors, molluscicides, nematicides, plant activators, plant-growthregulators, rodenticides, synergists, and virucides.

Additional aspects and advantages of this invention will be apparentfrom the following detailed description of preferred embodiments.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention generally relates to methods of and productsformed by entrapping a bioactive, growth-promoting additive in a starchmatrix to form a starch-based SAP product for use in agriculturalapplications. When applied to a growing substrate in proximity to aplant, root, seed, or seedling, or directly to a plant, root, seed, orseedling, the starch-based SAP product including a bioactive,growth-promoting additive promotes growth of a plant, root, seed, orseedling placed in proximity to the SAP product by promoting theavailability of beneficial nutrients to the plant, root, seed, orseedling. The high absorptivity of the starch matrix of the starch-basedSAP product facilitates entrapment of the bioactive, growth-promotingadditive in the starch matrix, thereby minimizing or eliminatingdisassociation or release of the bioactive, growth-promoting additivefrom the starch matrix due to heavy rainfall, squeezing, or jarring ofthe SAP product during transport or manufacture, and during applicationof the SAP product. Because the bioactive, growth-promoting additive isentrapped in the SAP product, the runoff rate of the growth-promotingadditive is significantly less than the runoff rate of growth-promotingadditives applied directly to soil, plants, roots, seedlings, or seeds.

The terms “entrapped” and “encapsulated” as used herein are meant torefer to the fact that the bioactive, growth-promoting additive isphysically held by the starch matrix portion of the SAP product. Theterm “bioactive, growth-promoting additive” is meant to include anyadditive that promotes plant, root, seedling, or seed growth.Indications of promotion of growth include, but are not limited to,earlier seed germination and/or blooming, decreased irrigationrequirements, increased propagation, increased crop growth, increasedcrop production, increased plant size, increased crop yield, anddecreased soil crusting

A preferred method of forming an SAP product including a bioactive,growth-promoting additive for use in agricultural applications involves(1) graft polymerizing at least one grafting reagent and a starch toform a starch graft copolymer including a starch matrix; (2) isolatingthe resulting starch graft copolymer; (3) forming particles of starchgraft copolymer that are sized for use in agricultural applications; and(4) adding the bioactive, growth-promoting additive so that at leastsome of the bioactive, growth-promoting additive is entrapped by thestarch matrix. Addition of the bioactive, growth-promoting additive mayoccur at various times during this process, depending on the type ofadditive and the desired degree of entrapment of the additive within thestarch matrix.

There are at least two preferred implementations of this preferredmethod of making a starch-based SAP product including a bioactive,growth-promoting additive for use in agricultural applications. A firstpreferred implementation involves (1) combining a monomer and a starchin the presence of an initiator such that the monomer graft polymerizesonto the starch to form a mixture including a starch graft copolymerhaving a starch matrix; (2) saponifying the mixture; (3) precipitatingthe saponified starch graft copolymer from the mixture to form particlesof SAP product that are sized for use in agricultural applications; and(4) adding the bioactive, growth-promoting additive so that it isentrapped in the starch matrix. Addition of the bioactive,growth-promoting additive may occur, for example, during at least one ofthe following processing steps: (1) while combining the monomer and thestarch; (2) following saponification of the mixture; and (3) followingformation of particles of starch-based SAP product.

With respect to this first preferred implementation, an exemplarypreferred monomer is acrylonitrile. The acrylonitrile may be used aloneor in conjunction with other monomers, such as, for example,2-acrylonitrile-2-methyl-propanesulfonic acid, acrylic acid, andacrylamide. These monomers may also be used instead of thepolyacrylonitrile. A preferred molar ratio of starch to acrylonitrile isbetween about 1:1 and about 1:6, and the amount of acrylonitrile in theSAP product is typically proportional to absorbency of the SAP product.

The acrylonitrile is preferably graft polymerized onto the starch in thepresence of an initiator, such as a cerium salt. Exemplary preferredcerium salts include, but are not limited to, ceric ammonium nitrate,ammonium persulfate, sodium persulfate, potassium persulfate, ferrousperoxide, ferous ammonium sulfate-hydrogen peroxide, L-ascorbic acid,potassium permanganate-ascorbic acid, derivatives thereof, and mixturesthereof. The graft polymerization process is typically complete withinseveral minutes, producing long, grafted chains of polyacrylonitrile, orpolyacrylonitrile in conjunction with other monomers, attached to thestarch.

The long, grafted chains of polyacrylonitrile, or polyacrylonitrile inconjunction with other monomers, attached to the starch are thensaponified, preferably with potassium hydroxide or sodium hydroxide, tochange the nitrile groups into a mixture of carboxamides and alkalicarboxylates. Saponification produces a highly viscous mass ofsaponificate having a dough-like consistency.

The saponificate (either with or without the bioactive, growth-promotingadditive) is then precipitated into solid form using a water-misciblesolvent such as an alcohol, e.g., methanol, ethanol, propanol, orisopropanol. Since methanol is generally the least expensive alcohol, itis typically preferred. The saponificate is immersed in alcohol, causingthe alkali starch graft copolymer to precipitate, forming particles thatmay be dried and screened to the desired size. The alcohol removes waterfrom, desalts, and granularizes the neutralized starch graft copolymersaponificate. Various precipitation methods using an alcohol exist andcould be used in connection with the present invention. Exemplarypreferred precipitation methods are discussed in greater detail below.

A second preferred implementation involves (1) combining a monomer and astarch in the presence of an initiator such that the monomer graftpolymerizes onto the starch to form a mixture including a starch graftcopolymer having a starch matrix; (2) adding a cross-linking agent tothe mixture to form a cross-linked starch graft copolymer; (3)neutralizing the mixture; (4) forming particles of SAP product that aresized for use in agricultural applications; and (5) adding thebioactive, growth-promoting additive so that at least some of it isentrapped in the starch matrix. Addition of the bioactive,growth-promoting additive may occur, for example, during at least one ofthe following processing steps: (1) while graft polymerizing the monomeronto the starch; (2) following neutralization; and (3) followingformation of the particles of starch-based SAP product.

With respect to this second preferred implementation, exemplarypreferred monomers include, but are not limited to, acrylic acid,acrylamide, methacrylamide, 2-acrylonitrile-2-methyl-propanesulfonicacid, methacrylic acid, vinyl sulfonic acid, ethyl acrylate, derivativesthereof, and mixtures thereof.

The monomer is preferably graft polymerized onto the starch in thepresence of an initiator. Exemplary initiators for use in theabove-described method include cerium (+4) salts, such as ceric ammoniumnitrate; ammonium persulfate; sodium persulfate; potassium persulfate;ferrous peroxide; ferrous ammonium sulfate-hydrogen peroxide; L-ascorbicacid; and potassium permanganate-ascorbic acid. Other suitableinitiators known to those skilled in the art may be used. The amount ofinitiator used will vary based on the chosen initiator, the chosenmonomer, and the chosen starch. Some initiators, e.g., persulfates,require the presence of heat. The initiator may be added in a single ormultiple steps, and multiple initiators may be used.

Next, a cross-linking agent is added to the mixture to form across-linked starch graft copolymer. A cross-linking agent is neededbecause unless the starch graft copolymer is cross-linked, it maydissolve in aqueous fluid. Cross-linking permits the starch graftcopolymer to absorb aqueous fluid without dissolving. The amount ofcross-linking agent added is indirectly proportional to the absorbencyof the resulting SAP product. Exemplary preferred cross-linking agentsinclude glycerides; diepoxides; diglycidyls; cyclohexadiamide; methylenebis-acrylamide; bishydroxyalkylamides, such as bis hydroxypropyladipamide; formaldehydes, such as urea-formaldehyde andmelamine-formaldehyde resins; isocyanates including di- andtri-isocyanates; epoxy resins, typically in the presence of a basecatalyst; derivatives thereof, and mixtures thereof.

Although the use of a cross-linking agent is preferred,self-cross-linking copolymers may also be used. If a self-cross-linkingcopolymer is used, either a single or multiple self-reactive functionalgroup(s) or multiple co-reactive functional groups are incorporated intothe mixture. One exemplary co-reactive functional group is glycidylmethacrylate.

Once a cross-linked starch graft copolymer is formed, the cross-linkedstarch graft copolymer is neutralized to convert the carboxyl groups topotassium salts, where, for example, potassium hydroxide or potassiummethoxide is used to neutralize the starch graft copolymer. In contrastto prior art methods, which require saponification, the neutralizationstep of the present invention is significantly faster, easier, and lessexpensive. Also, neutralization does not produce corrosive and dangerousreaction by-products such as ammonia. Exemplary solvents that may beused to effect neutralization include potassium hydroxide, potassiummethoxide, and a mixture thereof, any of which may be diluted inmethanol.

The resulting neutralized, cross-linked starch graft copolymer is thenisolated or precipitated to form particles of SAP product. Exemplarypreferred isolation and precipitation methods are discussed in greaterdetail below. Isolation may occur by any method known to those ofordinary skill in the art, including (1) extrusion and drying, forexample, on a double drum dryer, (2) drying the neutralized dough on adouble drum dryer to form flakes of the SAP product and later formingparticles of the desired size from the flakes of SAP product, (3) traydrying the neutralized dough to form flakes of the SAP product and laterforming particles of the desired size from the flakes of SAP product,and (4) forming particles from the neutralized dough and then traydrying these particles.

With respect to both the first and second preferred implementations, thebioactive, growth-promoting additive is preferably added to the SAPdough or particles such that it is substantially distributed throughout.One exemplary preferred method by which addition of the bioactive,growth-promoting additive may occur involves dissolving the additive ina solvent and then spraying the solution of growth-promoting additiveonto the SAP dough or onto the particles of SAP product (with or withoutagitation of the dough or particles during addition). A second preferredmethod of adding the bioactive, growth-promoting additive involvesforming a slurry of additive and adding the slurry to the SAP dough orparticles at any point during processing. One advantage of adding thebioactive, growth-promoting additive following formation of theparticles of SAP product is that the highly absorptive nature of theparticles results in their readily imbibing the additive. In onepreferred embodiment, the particles of starch-based SAP product aredried following application of the additive.

Bioactive, growth-promoting additives generally fall into one of twocategories: water-soluble additives and water-insoluble additives.Water-soluble additives can be added directly to the SAP dough orparticles at any point during processing or during application of theSAP product to the growing substrate. When using the first preferredimplementation of the preferred method, the water-soluble additives arepreferably added to the SAP dough following saponification or followingformation of the particles of SAP product, because addition of thebioactive, growth-promoting additive during combination of the graftingreagent(s) and the starch may result in the additive being washed outduring saponification.

Water-insoluble, bioactive, growth-promoting additives can be added atany point during processing, to the SAP particles, or during applicationof the SAP product to the growing substrate. Typically, water-insolubleadditives are dissolved in a solvent, e.g., a water-miscible solventsuch as alcohol, and then the solution is applied to the SAP dough, SAPparticles, or to the growing substrate. Following application of thesolution or slurry of dissolved bioactive, growth-promoting additive,the solvent may be removed from the SAP dough or particles by heating ordrying to drive off residual solvent by evaporation.

A preferred proportion of bioactive, growth-promoting additive per poundof SAP product is about 1 oz. per lb. Exemplary bioactive,growth-promoting additives include fertilizers, plant-growth regulators,pesticides, plant-growth hormones, and soil-based nutrients, all ofwhich may be in solid, crystalline, aqueous, or fluid form.

A list of exemplary pesticides includes acaricides, algicides,antifeedants, avicides, bactericides, bird repellents, chemosterilants,fungicides, herbicide safeners, herbicides, insect attractants, insectrepellents, insecticides, mammal repellents, mating disruptors,molluscicides, nematicides, plant activators, plant-growth regulators,rodenticides, synergists, virucides, derivatives thereof, blendsthereof, and combinations thereof. Three exemplary commerciallyavailable pesticides are as follows: Asset™, manufactured by HelenaChemicals of Fairfax, S.C.; ACA™, manufactured by UAP of Greeley, Colo.;and Miracle-Gro™, manufactured by the Scotts Company of Marysville,Ohio.

Exemplary plant-growth regulators include antiauxins, such as, forexample, 2,3,5-tri-iodobenzoic acid; auxins, such as, for example,2,4-D; cytokinins, such as, for example, kinetin; defoliants, such as,for example, metoxuron; ethylene inhibitors; ethylene releasers, suchas, for example, ACC and gloxime; gibberellins; growth inhibitors;growth retardants; growth stimulants; derivatives thereof; and mixturesthereof.

A list of exemplary preferred herbicides is as follows: amide herbicidesincluding chloroacetanilide herbicides (such as alachlor andmetolachlor); antibiotic herbicides; aromatic acid herbicides includingbenzoic acid herbicides (such as chloramben and dicamba), phthalic acidherbicides, picolinic acid herbicides, and quinolinecarboxylic acidherbicides; arsenical herbicides; benzoylcyclohexanedione herbicides;benzofuranyl alkylsulfonate herbicides; carbamate herbicides;carbanilate herbicides; cyclohexene oxime herbicides;cyclopropylisoxazole herbicides; dicarboximide herbicides;dinitroaniline herbicides (such as trifluralin and pendimethalin);dinitrophenol herbicides; diphenyl ether herbicides; dithiocarbamateherbicides; halogenated aliphatic herbicides; imidazolinone herbicides;inorganic herbicides; nitrile herbicides; organophosphorus herbicides;phenoxy herbicides (such as 2-4D (also called 2,4-dichlorophenoxy aceticacid) and Mecoprop); phenylenediamine herbicides;pyrazolyloxyacetophenone herbicides; pyrazolylphenyl herbicides;pyridazine herbicides; pyridazinone herbicides (such as Norflurazon™);pyridine herbicides; pyrimidinediamine herbicides; quaternary ammoniumherbicides; thiocarbamate herbicides (including butylate and EPTC);thiocarbonate herbicides; thiourea herbicides; triazine herbicides (suchas atrazine and simazine); triazinone herbicides (such as Metribuzin™);triazole herbicides; triazolone herbicides; triazolopyrimidineherbicides; uracil herbicides; urea herbicides; Roundup™ (manufacturedby Monsanto Co. of St. Louis, Mo.); Chloropropham™; Surflan™(manufactured by Southern Agricultural Insecticides, Inc. of Palmetto,Fla.); and Clomazone™. A combination or blend of these herbicides may beused.

Exemplary microbial pesticides include bacillus thuringiensis andmycorrhizal fungi. Exemplary insecticides include thiodan, diazinon, andmalathion. Exemplary fungicides include Aliette™ (activeingredient=aluminum tris (o-ethylphosphenate)) manufactured by BayerCrop Science of Research Triangle Park, N.C.; Rovral™ (activeingredient=iprodione) manufactured by Bayer Crop Science of ResearchTriangle Park, N.C.; Mancozeb™; Sovran™ (activeingredient=kresoxim-methyl) manufactured by BASF Agolutions of Canada;Flint™ (active ingredient=trifloxystrobin) manufactured by NovartisCorporation; Ridomil™ (active ingredient=Mefenoxam) and Ridomil Gold™(active ingredient methoxyacetylamino-®-2-2[2,6-dimethylphenyl-propionicacid methyl ester] manufactured by Syngenta Crop Protection Inc. ofGreensboro, N.C.; Dividend™ (active ingredient=difenoconazole)manufactured by Syngenta Crop Protection Inc. of Greensboro, N.C.;SoilGard™ (active ingredient=gliocladium virens) manufactured by CertisUSA of Columbia, Md.; Bravo™ (active ingredient=chlorothalonil)manufactured by Syngenta Crop Protection Inc. of Greensboro, N.C.;Vitavax™ (active ingredient=carboxin) manufactured by Gustafson LLC ofCanada; Thiram™ (active ingredient=tetramethylthiuram disulfide)manufactured by Gustafson LLC of Canada; Maxim™ (activeingredient=fludioxonil) manufactured by Syngenta Crop Protection Inc. ofGreensboro, N.C.; Quadris™ (active ingredient=azoxystrobin) manufacturedby Syngenta Crop Protection Inc. of Greensboro, N.C.; and Elite™ (activeingredient=tebuconazole) manufactured by Bayer Crop Science of ResearchTriangle Park, N.C. A combination or blend of these may be used.

A list of exemplary soil-based nutrients includes calcium, magnesium,potassium, phosphorus, boron, zinc, manganese, copper, iron, sulfur,nitrogen, molybdenum, ammonium phosphate, fish meal, derivativesthereof, blends thereof, and mixtures thereof. More information aboutexemplary growth-promoting additives can be found in The Farm ChemicalsHandbook published by Meister Publishing Company, 1992.

Exemplary starches for use in connection with the above-identifiedmethods include pure starches, flours, and meals. Preferred starchesinclude cornstarch, corn meal, wheat starch, sorghum starch, tapiocastarch, cereal flours and meals, banana flour, yucca flour, peeled yuccaroot, unpeeled yucca root, oat flour, banana flour, and tapioca flour.Combinations, derivatives, and blends of these starches may also beused. These starch sources are preferably gelatinized to optimizeabsorbency. Exemplary commercially available starches include nativestarches (e.g., corn starch (e.g., Pure Food Powder™, manufactured byA.E. Staley), waxy maize starch (e.g., Waxy™ 7350, manufactured by A.E.Staley), wheat starch (e.g., Midsol™ 50, manufactured by Midwest GrainProducts), and potato starch (e.g., Avebe™, manufactured by A.E.Staley)), dextrin starches (e.g., Stadex™ 9, manufactured by A.E.Staley), dextran starches (e.g., Grade 2P, manufactured by PharmachemCorp.), corn meal, peeled yucca root, unpeeled yucca root, oat flour,banana flour, tapioca flour, and industrial-grade unmodified cornstarch.A preferred molar ratio of the starch to the monomer is between about1:1 and about 1:6.

As mentioned above, various preferred isolation methods can be used inconnection with the present invention. Isolation can occur byprecipitation or by drying and/or manipulation of the SAP dough.Precipitation can be used to form particles, granules, powders, strands,rods, films, and the like, all of which are referred to herein as“particles.” Some preferred precipitation methods involve adding awater-miscible solvent such as, for example, an alcohol, e.g., methanol,ethanol, propanol, or isopropanol. One preferred method of alcohol-basedprecipitation involves immersing the starch graft copolymer in alcohol,thereby causing the starch graft copolymer to precipitate into particlesthat are later screened to the desired size after drying. The alcoholremoves the water from, removes extraneous salts from, and granularizesthe starch graft copolymer.

A second preferred method of alcohol-based precipitation involvesblending sufficient alcohol into the starch graft copolymer to achieve asmooth dispersion. The smooth dispersion is then pumped into aprecipitation tank including a stirring system that can vigorously mixthe alcohol while the smooth starch graft copolymer dispersion is added.Once mixed, the resulting alcohol and starch graft copolymer particlesare either (1) collected by decanting or washing with alcohol or (2)centrifuged and collected, then dried to a moisture level of betweenabout 1 percent and about 20 percent.

A third preferred method of alcohol-based precipitation involves wettingthe surface of the saponificate or neutralized starch graft copolymerwith a small amount of alcohol and then chopping the starch graftcopolymer into larger “chunks” that will not re-adhere to one another.Once the surface of the saponificate or neutralized starch graftcopolymer has been wetted with alcohol, the resulting material isslippery to the touch and is no longer sticky. This effect may beachieved, for example, by using a compositional ratio of between aboutone part and about two parts of methanol per one part of solid. Once thealcohol has been added, the saponificate or neutralized starch graftcopolymer is either (1) pumped through an in-line chopper to form chunkshaving a diameter of less than one inch or (2) hand-chopped withscissors. The resulting mixture is then fed into a tank or Waringblender that has between about 1.5 gallons and about 2.0 gallons ofadditional alcohol per pound of starch graft copolymer. The alcohol inthe larger tank is agitated with a Cowles dissolver or other mixercapable of achieving high speeds.

A fourth preferred method of alcohol-based precipitation involvespre-forming the particle size before the alcohol-based precipitation.The use of dies to form strands or rods having different shapes anddiameters can greatly improve the particle-size formation process. Thisfourth method offers enhanced control of the final particle size. Thestarch graft copolymer (neutralized or unneutralized) is forced througha die plate having holes of varying diameter (e.g., about {fraction(1/16)} inch to more than ¼ inch) and varying shape (e.g., round, star,ribbon, etc.). Methods of forcing the starch graft copolymer through thedie plate include using a hand-operated plunger, screw-feeding,auguring, pumping, and any other commonly known method. The resultingstrands or rods are placed into the precipitation tank without anyfurther addition of alcohol as a premixing agent. The strands or rodsmay be treated to prevent them from sticking together, by, for example,wetting the strands or rods with alcohol or dusting them with a dustingagent, such as, for example, cellulose, clay, starch, flour, or othernatural or synthetic polymers. Alternatively, the strands or rods may belightly sprayed with alcohol to prevent them from sticking together. Theresulting strands or rods are precipitated with agitated alcohol,removed from the tank, and dried.

A exemplary method of isolating the starch graft copolymer that does notinvolve adding alcohol involves drying the starch graft copolymer on aheated drum or via air-drying. The resulting particles of SAP produceare then manipulated to form a final SAP product having a size and formappropriate for the desired agricultural application. Because the secondpreferred implementation of the method of forming an SAP productincluding a bioactive, growth-promoting additive forms a neutralized,cross-linked starch graft copolymer that is a relatively pure systemcontaining very little extraneous salt, isolation of the SAP productformed using this implementation can be effected by merely drying theSAP product. In contrast, prior art starch graft copolymers contain asignificant amount of extraneous salt and ammonia and thus must betreated with an alcohol, typically methanol. The use of methanolsignificantly adds to the cost of producing the SAP product becausemethanol disposal is very expensive.

Another exemplary method of isolating the starch graft copolymer withoutadding alcohol involves extruding the neutralized, cross-linked starchgraft copolymer through a heated screw to form particles of SAP product.To minimize re-agglomeration of the particles, the particles arepreferably coated with a dusting agent that decreases their propensityto stick together. Exemplary dusting agents include cellulose, clay,starch, flour, and other natural or synthetic polymers that prevent theparticles from sticking together. Alternatively, the particles may belightly sprayed with methanol to prevent them from sticking together,and/or the extrusion can be performed under high pressure.

Where the SAP product is used in particle form, the preferred particlesize of the starch-based SAP product depends on the specificagricultural application intended. A preferred particle size foragricultural applications that deposit the starch-based SAP productdirectly onto the growing substrate is less than 50 mesh, moreparticularly between about 8 mesh and about 25 mesh. This particle sizeis preferred because commercially available granular applicators requirethis particle size. To broadcast or meter the starch-based SAP particlesthrough existing agricultural application equipment, an 8-mesh to about25-mesh granular, starch-based SAP product having a density of betweenabout 25 lbs per cubic foot and about 35 lbs per cubic foot, with 32 lbsper cubic foot most preferred.

Other agricultural applications, such as seed coating and root dipping,use a finer particle size. For seed coating, the desired particle sizeis between about 75 mesh and about 200 mesh, more preferably about 100mesh. For root coating, the desired particle size is between about 30mesh and about 100 mesh, more preferably about 50 mesh. Further, therelease rate of the starch-based SAP product is affected by its particlesize. For example, preliminary results suggest that pelletized particlesmay release the active portion of the bioactive, growth-promotingadditive more gradually than granular products of equal surface area.

Fillers, absorbents, carriers, and surfactants whose presence affectsthe processability or efficacy of the bioactive, growth-promotingadditive may be used to form the starch-based SAP product. Exemplarycarriers include Kaolin clay, Fullers Earth, diatomaceous earthproducts, ungelatinized granular starch, silicates, blends thereof,mixtures thereof, and derivatives thereof. Typically, the swellabilityof the starch-based SAP product decreases with increased proportions ofclay. The processing point at which the fillers, absorbents, carrier,and surfactants are added may vary depending upon the desiredcharacteristics of the resulting SAP product. Two exemplary preferredpoints of addition of a filler, absorbent, carrier, or surfactant are(1) preblending with the starch and (2) separate addition duringdownstream processing.

SAP products including a bioactive, growth-promoting additive may beused in connection with any crop. A list of exemplary crops is asfollows: alfalfa, asparagus, barley, beans (including lima beans, snapbeans, and green beans), broccoli, canola, carrots, cauliflower, celery,coriander, coreopsis, cotton, cucumbers, dill, elymus glaucus, fieldcorn (including sweet corn), fine fescue, garlic, kentucky bluegrass,lentils, lettuce (including mesclin, head lettuce, leaf lettuce, romainelettuce, and cabbage), oats, onions, melons (including watermelon,cantaloupe, and honeydew), mushrooms, parsley, peas (dry), peppers(including bell peppers), potatoes, pumpkins, radishes, rye grass, sod,sorghum, soybeans, spinach, squash, sugar beets, sunflowers, Swisschard, tall fescue, tobacco, tomatoes, turnips, wheat, white clover,wild rye, and zinnia.

Application of the SAP product to a plant, root, seed, or seedling mayoccur by any method known to one of ordinary skill, including, but notlimited to, dipping the plant, root, seed, or seedling into SAP productparticles, a slurry of SAP product particles, or a paste including theSAP product particles; mixing dirt, soil, fertilizer, or another growingsubstrate with the SAP product particles and later planting a plant,root, seed, or seedling into the growing substrate/SAP product mixture;and forming a slurry of SAP product that is applied directly to thegrowing substrate.

Preferred exemplary methods of using the starch-based SAP productincluding a bioactive, growth-promoting additive to promote plant, seed,seedling, or root growth include (1) placing the starch-based SAPproduct including a bioactive, growth-promoting additive (or a slurry,mat, or fertilizer including the SAP product) directly onto a growingsubstrate in proximity to a plant, seed, seedling, or root and (2)applying to a plant, seed, seedling, or root the starch-based SAPproduct (or a slurry or fertilizer including the SAP product) and thenplanting the plant, root, seed, or seedling in the growing substrate.One exemplary method of preparing a slurry for use as a root dipinvolves combining between about 3 oz. and about 6 oz. of SAP productwith about 5 gallons of water to form a slurry that is applied to thegrowing substrate and/or to the plant, root, seed, or seedling. Oneexemplary method of preparing a seed coating including the SAP productinvolves combining a binding agent and the SAP product with a solvent,preferably water, to form a slurry that is applied to the seed.Alternatively, the dry SAP product may be combined with a binder ortackifier, such as, for example, a mineral, gypsum, or clay, to form amixture that will stick to the seed. These methods can also be used toprepare a coating to be applied to any of a plant, root, seed, orseedling.

The inventors of the present invention recognize that entrapmentefficiency, swellability, release rate, and efficacy of the starch-basedSAP product can be affected to various degrees by the types of materialsused, the processing conditions implemented, and the degree and type ofex-situ downstream processing. Because composition and processingconditions are selected to maximize product performance and processingefficiency, preferred processing parameters, such as, for example,temperature, solids concentration, concentration of starch,concentration of growth-promoting additive, type of additive, number ofadditives, levels of addition, addition processes, and addition timing,vary greatly. For this reason, the following examples are intended onlyto further illustrate the invention and are not intended to limit thescope of the invention.

EXAMPLE 1 Spray Application of Asset™ Pesticide to SAP Particles

Distilled water (1,400 ml) was placed in a 3-liter resin kettle and wassubjected to constant agitation with a stirrer. Starch flour or meal(110 g) was slowly added to the kettle, and the resulting mixture wasstirred for approximately five minutes. A slow stream of nitrogen gaswas added to the mixture while the mixture was heated until it reached atemperature of approximately 95° C. Upon reaching this temperature, themixture was maintained at this temperature and stirred for approximately45 minutes to ensure that the starch was gelatinized. The heating mantlewas then removed, and the resin kettle was placed in a cold-water bucketbath. The mixture was continuously stirred under nitrogen until thetemperature reached 25° C. Acrylonitrile (115 g) and2-acrylamido-2-methyl-propanesulfonic acid (23 g) were added. Theresulting mixture was continuously stirred under nitrogen forapproximately 10 minutes. A catalyst solution including cerium ammoniumnitrate (5.5 g) dissolved in 0.1 M nitric acid solution (50 ml) wasadded to the mixture while the mixture cooled. The mixture wascontinuously stirred under nitrogen while the resin kettle remained inthe cold-water bucket for approximately 60 minutes. The temperature ofthe mixture at the end of the 60 minutes was approximately 40° C. Asolution including potassium hydroxide flakes (90 g) dissolved in water(200 g) was added to the mixture during stirring and heating. Themixture was stirred and heated until a temperature of 95° C. wasachieved, after which the mixture was stirred for an additional 60minutes. The mixture was then neutralized to a pH of 7.5 using a 10%solution of hydrochloric acid. The resulting dough was then cooled to atemperature of about 40° C. The viscous dough was precipitated inmethanol using one of the above-described precipitation methods toproduce SAP particles.

The resulting SAP particles were subjected to a Fertilizer Analysis Testthat analyzed the presence of various bioactive components. The resultsare reproduced in Table I to allow the reader to compare the SAP productwith the starch-based SAP product of the present invention. TABLE IFertilizer Analysis of an SAP Product Without an Additive. Nutrient %Available Nitrogen 3.04 Ammonia <0.01 Phosphorus <0.10 P₂O₅ N/APotassium 17.66 K₂O 21.28 Calcium <0.01 Magnesium <0.01 Sodium 0.08Boron <20.0 Iron 39.96 Manganese <10.0 Copper <10.0 Zinc <10.0Monoammonium Phosphate N/ATrial A: Application of Asset™ Pesticide at a Concentration of 3Pints/Acre

Using a standard, commercially available garden sprayer, approximately 3pints of Asset™ was sprayed onto 10 lbs. of SAP product having a meshsize of between about 10 and about 20 and formed using theabove-described method. The SAP particles were agitated duringapplication of the Asset™ pesticide, to ensure that the bioactive,growth-promoting additive thoroughly coated the SAP particles. Asset™pesticide has a slight green tint, and thus the application of Asset™pesticide to the SAP particles resulted in their being slightly tintedgreen. The resulting starch-based SAP particles were subjected to aFertilizer Analysis Test that analyzed the presence of various bioactivecomponents. The results are reproduced in Table II. TABLE II FertilizerAnalysis of the SAP Product Formed in Trial A. Nutrient % AvailableNitrogen 3.85 Ammonia 0.13 Phosphorus 2.61 P₂O₅ 5.97 Potassium 16.06 K₂O19.35 Calcium <0.01 Magnesium <0.01 Sodium 0.13 Boron 74.08 Iron 288.93Manganese 165.65 Copper 151.97 Zinc 160.67 Monoammonium Phosphate 1.07Trial B: Application of Asset™ Pesticide at a Concentration of 8Pints/Acre

Using a standard, commercially available garden sprayer, approximately 8pints of Asset™ pesticide was sprayed onto 10 lbs of SAP product havinga mesh size of between about 10 and about 20 and formed using theabove-described method. The SAP particles were agitated duringapplication of the Asset™ pesticide, to ensure that the bioactive,growth-promoting additive thoroughly coated the SAP particles. Asset™pesticide has a slightly green tint, and thus the application of Asset™pesticide to the SAP particles resulted in their being slightly tintedgreen. The resulting starch-based SAP particles were subjected to aFertilizer Analysis Test that analyzed the presence of various bioactivecomponents. The results are reproduced in Table III. TABLE IIIFertilizer Analysis of the SAP Product Formed in Trial B. Nutrient %Available Nitrogen 4.76 Ammonia 0.62 Phosphorus 5.90 P₂O₅ 13.51Potassium 15.07 K₂O 18.16 Calcium <0.01 Magnesium <0.01 Sodium 0.20Boron 166.17 Iron 629.38 Manganese 373.84 Copper 340.36 Zinc 353.38Monoammonium Phosphate 5.09

EXAMPLE 2 Slurry Application of Asset™ Pesticide to SAP Particles

SAP particles having a mesh size of between about 20 and about 40 weremade according to the method described in Example 1. Approximately 25 gof SAP particles were combined with 1 L of an aqueous slurry of Asset™pesticide. The resulting slightly green-tinted slurry was agitated toensure that the Asset™ pesticide was evenly distributed throughout theslurry. The slurry was subjected to a Fertilizer Analysis Test thatanalyzed the presence of various bioactive components. The results arereproduced in Table IV. TABLE IV Fertilizer Analysis of the SAP Productof Example 2. Nutrient % Available Nitrogen 5.66 Ammonia 2.47 Phosphorus7.96 P₂O₅ 18.24 Potassium 3.94 K₂O 4.74 Calcium <0.01 Magnesium <0.01Sodium 0.18 Boron 219.79 Iron 847.58 Manganese 673.47 Copper 452.49 Zinc462.74 Monoammonium Phosphate 20.28

EXAMPLE 3 Spray Application of Miracle-Gro™ Pesticide to SAP Particles

SAP particles having a mesh size of between about 10 and about 20 weremade according to the method described in Example 1. Between about 6pints and about 8 pints of Miracle-Gro™ pesticide was sprayed onto about1 lb. of SAP product using a standard, commercially available gardensprayer. The resulting particles of starch-based SAP product wereagitated to ensure that the Miracle-Gro™ pesticide was evenlydistributed. Following spraying, the SAP particles were slightly tintedgreen.

EXAMPLE 4 Inclusion of Miracle-Gro™ Pesticide in the SAP Dough

Distilled water (1,400 ml) was placed in a 3-liter resin kettle and wassubjected to constant agitation with a stirrer. Starch flour or meal(110 g) was slowly added to the kettle, and the resulting mixture wasstirred for approximately five minutes. A slow stream of nitrogen gaswas added to the mixture while the mixture was heated until it reached atemperature of approximately 95° C. The mixture was maintained at thistemperature and stirred for approximately 45 minutes to ensure that thestarch was gelatinized. The heating mantle was then removed, and theresin kettle was placed in a cold-water bath. The mixture wascontinuously stirred under nitrogen until the temperature reached 25° C.Acrylonitrile (115 g) and 2-acrylamido-2-methyl-propanesulfonic acid (23g) were added. The resulting mixture was continuously stirred undernitrogen for approximately 10 minutes. A catalyst solution includingcerium ammonium nitrate (5.5 g) dissolved in 0.1M nitric acid solution(50 ml) was added to the mixture while the mixture cooled. The mixturewas continuously stirred under nitrogen while the resin kettle remainedin the cold-water bath for approximately 60 minutes. The temperature ofthe mixture at the end of the 60 minutes was approximately 40° C. Asolution including potassium hydroxide flakes (90 g) dissolved in water(200 g) was added to the mixture during stirring and heating. Themixture was stirred and heated until a temperature of 95° C. wasachieved, after which the mixture was stirred for an additional 60minutes. The mixture was then neutralized to a pH of 7.5 using a 10%solution of hydrochloric acid. The dough was then cooled to atemperature of about 40° C. Approximately 12 pints of liquidMiracle-Gro™ pesticide was added to about one lb. of dough. Theresulting slightly green-tinted dough was agitated for approximately 30minutes to ensure intimate mixing of the Miracle-Gro™ pesticide and theSAP dough. The resulting dough was extruded into granules. In oneimplementation, a pasta maker was used to extrude rod-shaped granules.Following extrusion, the granules were dried. Because the rod-shapedgranules were sticky, they were dusted with sufficient clay, starch,flour, cellulose, or celite to remove the stickiness. In oneimplementation, the rod-shaped granules were ground into particleshaving a desired particle size. Optionally, fine particles could beformed into pellets having a desired size. The process of pelletizing iswell known to those skilled in the art.

EXAMPLE 5 Inclusion of Ammonium Phosphate in the SAP Dough

Distilled water (1,400 ml) was placed in a 3-liter resin kettle and wassubjected to constant agitation with a stirrer. Starch flour or meal(115 g) was slowly added to the kettle, and the resulting mixture wasstirred for approximately five minutes. A slow stream of nitrogen gaswas added to the mixture while the mixture was heated until it reached atemperature of approximately 95° C. The mixture was maintained at thistemperature and stirred for approximately 45 minutes to ensure that thestarch was gelatinized. The heating mantle was then removed, and theresin kettle was placed in a cold-water bath. The mixture wascontinuously stirred under nitrogen until the temperature reached 25° C.Acrylonitrile (115 g) and 2-acrylamido-2-methyl-propanesulfonic acid (23g) were added. The resulting mixture was continuously stirred undernitrogen for approximately 10 minutes. A catalyst solution includingcerium ammonium nitrate (5.5 g) dissolved in 0.1M nitric acid solution(50 ml) was added to the mixture while the mixture was cooled. Themixture was continuously stirred under nitrogen while the resin kettleremained in the cold-water bath for approximately 60 minutes. Thetemperature of the mixture at the end of the 60 minutes wasapproximately 40° C. A solution including potassium hydroxide flakes (90g) dissolved in water (200 g) was added to the mixture during stirringand heating. The mixture was stirred and heated until a temperature of95° C. was achieved, after which the mixture was stirred for anadditional 60 minutes. The mixture was then neutralized to a pH of 7.5using a 10% solution of hydrochloric acid. The dough was then cooled toa temperature of about 40° C. Approximately 36.5 g of ammonium phosphatewas added directly to about one lb. of dough. The resulting dough wasagitated for approximately 30 minutes to ensure intimate mixing of theammonium phosphate and the SAP dough. The resulting dough was extrudedinto granules. In one implementation, a pasta maker was used to extruderod-shaped granules. Following extrusion, the granules were dried.Because the rod-shaped granules were sticky, they were dusted withsufficient clay, starch, flour, cellulose, or celite to remove thestickiness. In one implementation, the rod-shaped granules were groundinto particles having a desired particle size. Optionally, fineparticles could be formed into pellets having a desired size. Theprocess of pelletizing is well known to those skilled in the art.

In general, optimal levels of entrapment of bioactive, growth-promotingadditive occur when the starch is highly gelatinized by a combination ofmechanical and thermal energy, because a highly gelatinized starch willundergo a greater degree of hydrogen bonding than will a partiallygelatinized starch, resulting in a more gradual release rate. Incontrast, lower processing temperatures can be used to increase therelease rate of the granular, starch-based SAP product.

One benefit offered by the starch-based SAP product including abioactive, growth-promoting additive is that it excels at carryingnutrients to seedling, roots, seeds, and plants. Further, starchcontrolled-release matrices provide a reduction in leaching, groundwatercontamination, toxicity, odor, volatility, and decompositional problemscompared to prior art application of fertilizers not entrapped in astarch matrix. The abundant availability, low cost, and physical natureof starches (especially cornstarch) in the United States make thestarch-based SAP product including a bioactive, growth-promotingadditive relatively inexpensive to manufacture.

Another benefit of the starch-based SAP product including a bioactive,growth-promoting additive is that it provides controlled-releasetechnology designed to extend the period of time over which the activeportion of the bioactive, growth-promoting additive is released into agrowing environment. Two objectives of controlled release are (1) toimprove efficacy and (2) to reduce negative environmental consequencesof bioactive, growth-promoting additive application.

One advantage of the second preferred implementation of the method offorming the starch-based SAP product including a bioactive,growth-promoting additive is elimination of the saponification step.Saponification has various drawbacks. First, saponification requiresexpensive machinery and generates ammonia, which is corrosive, costly toremove, and expensive to dispose of. Second, the potassium hydroxide(KOH) added during saponification makes the saponified starch graftcopolymer mixture basic, and acid, e.g., hydrochloric acid, nitric acid,sulfuric acid, or phosphoric acid, must be added to the mixture in orderto neutralize the pH of the starch graft copolymer mixture. If theamount of acid that must be added is significant, the absorbency of theSAP is reduced. Third, the saponification waste solutions are expensiveto dispose of because they include potassium and ammonium salts andother extraneous salts. Fourth, acrylonitrile is hazardous to use andexpensive to dispose of.

In one preferred embodiment, the active portion of the bioactive,growth-promoting additive is withdrawn from the starch matrix bycapillary action of the plant, root, or seedling. In an alternativepreferred embodiment, seeds utilize the active portion of the bioactive,growth-promoting additive as it slowly diffuses from the starch matrix.One way that diffusion occurs is as follows: particles of the SAPproduct including a bioactive, growth-promoting additive imbibe water,swell, and thereby allow the active portion of the bioactive,growth-promoting additive entrapped in the starch matrix to slowlydiffuse out of the particles. Temperature and microbial activity canaffect the rate of release, including the rate of diffusion.

It will be obvious to those having skill in the art that many changesmay be made to the details of the above-described embodiments withoutdeparting from the underlying principles of the invention. The scope ofthe present invention should, therefore, be determined only by thefollowing claims.

1. A method of forming a superabsorbent polymer product including abioactive, growth-promoting additive for use in agriculturalapplications, comprising: combining a grafting reagent and a starch suchthat the grafting reagent graft polymerizes onto the starch to form amixture including starch graft copolymers, the starch graft copolymersforming a starch matrix; isolating the starch graft copolymers; formingparticles including the starch graft copolymers, the particles beingsized for use in agricultural applications; and adding the bioactive,growth-promoting additive such that at least some of the bioactive,growth-promoting additive is entrapped by the starch matrix.
 2. Themethod of claim 1, in which addition of the bioactive, growth-promotingadditive occurs while combining the grafting reagent and the starch toform the starch graft copolymers.
 3. The method of claim 1, in whichaddition of the bioactive, growth-promoting additive occurs whileisolating the starch graft copolymers.
 4. The method of claim 1, inwhich addition of the bioactive, growth-promoting additive involvesapplying the bioactive, growth-promoting additive to the particles. 5.The method of claim 1, further comprising: adding a cross-linking agentto the mixture to form cross-linked starch graft copolymers; andneutralizing the cross-linked starch graft copolymers.
 6. The method ofclaim 5, in which the cross-linking agent is selected from a groupconsisting essentially of glycerides, diepoxides, diglycidyls,cyclohexadiamide, methylene bis-acrylamide, bis-hydroxyalkylamides,bis-hydroxypropyl adipamide, formaldehydes, urea-formaldehyde,melamine-formaldehyde resins, isocyanates, di-isocyanates,tri-isocyanates, epoxy resins, self-cross-linking polymers, derivativesthereof, and mixtures thereof.
 7. The method of claim 1, furthercomprising: saponifying the mixture.
 8. The method of claim 1, in whichcombining the grafting reagent and the starch involves graftpolymerizing a monomer onto the starch in the presence of an initiator.9. The method of claim 8, in which the monomer is selected from a groupconsisting essentially of acrylonitrile, acrylic acid, acrylamide,2-acrylonitrile-2-methyl-propanesulfonic acid, methacrylamide,methacrylic acid, vinyl sulfonic acid, ethyl acrylate, derivativesthereof, and mixtures thereof.
 10. The method of claim 8, in which thestarch and the monomer are present in a molar ratio of between about 1:1and about 1:6.
 11. The method of claim 8, in which the initiator is acerium salt.
 12. The method of claim 1, in which the starch is selectedfrom a group consisting essentially of pure starches, flours, meals, andmixtures thereof.
 13. The method of claim 1, in which the starch is agelatinized starch.
 14. The method of claim 1, in which forming theparticles involves precipitating the starch graft copolymers by one of(1) adding to the mixture a sufficient amount of an alcohol to cause thestarch graft copolymers to form a precipitate, and (2) mechanicallymanipulating the mixture such that it forms a precipitate.
 15. Themethod of claim 1, in which forming the particles involves drying themixture.
 16. The method of claim 1, in which a ratio of bioactive,growth-promoting additive to starch is between about 0.5 oz.:1 lb. andabout 1.5 oz.:1 lb.
 17. The method of claim 1, in which the bioactive,growth-promoting additive is selected from a group consistingessentially of fertilizers, pesticides, bioactive materials,plant-growth hormones, plant-growth regulators, soil-based nutrients,derivatives thereof, and mixtures thereof.
 18. The method of claim 1,further comprising: adding a material selected from a group consistingessentially of fillers, absorbents, carriers, surfactants, derivativesthereof, and mixtures thereof.
 19. The method of claim 1, furthercomprising: applying the superabsorbent polymer product including thebioactive, growth-promoting additive to one of (1) a growing substratein proximity to one of a plant, seedling, root, and seed and (2) to oneof a plant, a seedling, a root, and a seed.
 20. A method of forming asuperabsorbent polymer product including a bioactive, growth-promotingadditive for use in agricultural applications, comprising: combining amonomer and a starch in the presence of an initiator such that themonomer graft polymerizes onto the starch to form a mixture includingstarch graft copolymers, the starch graft copolymers forming a starchmatrix; saponifying the mixture; precipitating the starch graftcopolymers from the saponified mixture to form particles ofsuperabsorbent polymer product sized for use in agriculturalapplications; and adding the bioactive, growth-promoting additive suchthat at least a portion of the bioactive, growth-promoting additive isentrapped by the starch matrix.
 21. The method of claim 20, in whichaddition of the bioactive, growth-promoting additive occurs whilecombining the monomer and the starch.
 22. The method of claim 20, inwhich addition of the bioactive, growth-promoting additive occurs whileprecipitating the starch graft copolymers.
 23. The method of claim 20,in which addition of the bioactive, growth-promoting additive involvesapplying the bioactive, growth-promoting additive to the particles ofsuperabsorbent polymer product.
 24. The method of claim 20, in which themonomer is selected from a group consisting essentially ofacrylonitrile, acrylic acid, acrylamide,2-acrylonitrile-2-methyl-propanesulfonic acid, methacrylamide,methacrylic acid, vinyl sulfonic acid, ethyl acrylate, derivativesthereof, and mixtures thereof.
 25. The method of claim 20, in which thestarch and the monomer are present in a molar ratio of between about 1:1and about 1:6.
 26. The method of claim 20, in which the initiator is acerium salt.
 27. The method of claim 20, in which the starch is selectedfrom a group consisting essentially of pure starches, flours, meals, andmixtures thereof.
 28. The method of claim 20, in which precipitating thestarch graft copolymers involves at least one of (1) adding a sufficientamount of an alcohol to the saponified mixture to cause it to form aprecipitate and (2) mechanically manipulating the saponified mixturesuch that it forms a precipitate.
 29. The method of claim 20, in whichthe bioactive, growth-promoting additive is selected from a groupconsisting essentially of fertilizers, pesticides, bioactive materials,plant-growth regulators, plant-growth hormones, soil-based nutrients,derivatives thereof, and mixtures thereof.
 30. The method of claim 20,further comprising: applying the particles of superabsorbent polymerproduct including the bioactive, growth-promoting additive to one of (1)a growing substrate in proximity to one of a plant, seedling, root, andseed and (2) to one of a plant, a seedling, a root, and a seed.
 31. Amethod of forming a superabsorbent polymer product including abioactive, growth-promoting additive for use in agriculturalapplications, comprising: combining a monomer and a starch in thepresence of an initiator such that the monomer graft polymerizes ontothe starch to form a mixture including starch graft copolymers, thestarch graft copolymers forming a starch matrix; adding a cross-linkingagent to the mixture to form cross-linked starch graft copolymers;neutralizing the mixture; forming particles of the superabsorbentpolymer product, the particles being sized for use in agriculturalapplications; and adding the bioactive, growth-promoting additive suchthat at least a portion of the bioactive, growth-promoting additive isentrapped by the starch matrix.
 32. The method of claim 31, in whichaddition of the bioactive, growth-promoting additive occurs whilecombining the monomer and the starch.
 33. The method of claim 31, inwhich addition of the bioactive, growth-promoting additive occurs whileforming the particles of superabsorbent polymer product.
 34. The methodof claim 31, in which addition of the bioactive, growth-promotingadditive involves applying the bioactive, growth-promoting additive tothe particles of superabsorbent polymer product.
 35. The method of claim31, in which the monomer is selected from a group consisting essentiallyof acrylonitrile, acrylic acid, acrylamide,2-acrylonitrile-2-methyl-propanesulfonic acid, methacrylamide,methacrylic acid, vinyl sulfonic acid, ethyl acrylate, derivativesthereof, and mixtures thereof.
 36. The method of claim 31, in which thestarch and the monomer are present in a molar ratio of between about 1:1and about 1:6.
 37. The method of claim 31, in which the initiator is acerium salt.
 38. The method of claim 31, in which the starch is selectedfrom a group consisting essentially of pure starches, flours, meals, andmixtures thereof.
 39. The method of claim 31, in which forming particlesof superabsorbent polymer product involves at least one of (1) adding asufficient amount of an alcohol to the mixture to cause it to form aprecipitate and (2) mechanically manipulating the mixture such that itforms a precipitate.
 40. The method of claim 31, in which the bioactive,growth-promoting additive is selected from a group consistingessentially of fertilizers, pesticides, bioactive materials,plant-growth hormones, plant-growth regulators, soil-based nutrients,derivatives thereof, and mixtures thereof.
 41. The method of claim 31,further comprising: applying the particles of superabsorbent polymerproduct including the bioactive, growth-promoting additive to one of (1)a growing substrate in proximity to one of a plant, seedling, root, andseed and (2) to one of a plant, a seedling, a root, and a seed.
 42. Asuperabsorbent polymer product whose use in agriculture promotes growthof a plant, root, seedling, or seed placed in proximity to thesuperabsorbent polymer product, comprising: a starch graft copolymermatrix; and a bioactive, growth-promoting additive, wherein thebioactive, growth-promoting additive is entrapped by the starch graftcopolymer matrix.
 43. The superabsorbent polymer product of claim 42, inwhich the starch graft copolymer matrix includes a starch selected froma group consisting essentially of pure starches, flours, meals,gelatinized starches, and mixtures thereof.
 44. The superabsorbentpolymer product of claim 42, in which particles of the superabsorbentpolymer product have a particle size that is about 200 mesh or less. 45.The superabsorbent polymer product of claim 42, in which particles ofthe superabsorbent polymer product have a particle size that is betweenabout 5 mesh and about 50 mesh.
 46. The superabsorbent polymer productof claim 42, in which particles of the superabsorbent polymer producthave a particle size that is between about 8 mesh and about 25 mesh. 47.The superabsorbent polymer product of claim 42, in which the bioactive,growth-promoting additive is selected from a group consistingessentially of fertilizers, pesticides, bioactive materials,plant-growth hormones, plant-growth regulators, soil-based nutrients,derivatives thereof, and mixtures thereof.